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Page 19
Example]
If 2 Byte data indicates 3A12 hex, the data is transmitted in the following order.
High order byte = 3A hex
Low order byte = 12 hex
Error Check Field
The error check field of a Modbus RTU packet enables you to check transmission errors that may
occur during communication using the CRC-16 algorithm. CRC-16 is two bytes[16 bits] long, and
the byte order features the
“Big Endian” format.
The slave device performs the same calculation on the entire packet it received, except for the error
check field. If the calculated result is not equal to the value of the error check field, it indicates that
transmission errors occurred. For more details of the CRC-16 algorithm, refer to the
“
Appendix A
&
B”
of this document.
Packet Format
Slave address
Function
Data
Error check
1 byte
1 byte
N
2 bytes
2 bytes
Exception Responses
If a master device sends an invalid command to the slave[Accura 7500] or attempts to read an
invalid holding register, an exception response will be generated from Accura 7500. To indicate an
error in the exception response, the high order bit of the function code is set to 1.
The data field of an exception response contains the exception error code.
Exception Response
Slave address
Function
Exception code
Error check
1 byte
1 byte
1 byte
2 bytes
Exception code
Name
Description
01
Illegal Function
Invalid command in Request Packet
02
Illegal Address
Invalid holding address in Request Packet
03
Illegal Value
Sends data invalid in Holding Address
Содержание ACCURA 7500
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